Re: ideal server

On Oct 17, 2008, at 2:19 PM, Brian Modra wrote:

> Hi,
> I have a server in production running postgresql, receiving 110 rows
> inserted per second, with some pretty intense queries involving long
> plpgsql.
> This server has 4Gigs of RAM and dual processor. Disk is Raid 5.
> I need more power, and am wondering what is the place really I need
> to put more emphasis? CPU, RAM, or disk?

Monitoring what your performance bottlenecks are on the current system
(after tuning postgresql reasonably) is probably the best way to get
an answer to that for your workload.

> I'm thinking of a 4xCPU and 20 Gigs and one of those large ram disks
> which has its own battery and writes all RAM to hard disk in the
> event of power failure.
>
> Obviously I need to first get a good sysadmin guy to configure
> postgres properly, but I am sure I also need a bigger host.
> Any advice will be appreciated.

Tune first. Then monitor. Then think about what hardware changes (or
system configuration changes) might be worth looking at.

I'm betting that at that point you'll find the problem is disk I/O,
but it may turn out not to be.

RAID5 isn't considered well suited to typical database I/O, compared
to RAID10 or similar.

At the moment you have system logging, database WAL and database data
all competing for the same I/O, meaning the drives are probably
seeking a lot. Some ways around that are to use a decent disk
controller with a (battery-backed) writeback cache to aggregate
writes, or to divide your disk traffic across different disks - for
instance, a dedicated RAID pair for the database WAL.

Cheers,
Steve